1. Field
The present invention relates to an imbalance detect method for use in a centrifuge which centrifuges samples stored in a rotor.
2. Description of the Related Art
As a centrifuge mainly for use in research and development for manufacture of drugs and reagents, generally, there is often used a centrifuge in which the rotation speed of a rotor is 20,000 rpm or more. In this type of centrifuge, a rotor, into which samples are to be stored and which is then rotated to separate the samples therein, is rotated at a high speed.
Samples to be centrifuged are respectively stored into tubes each having a small capacity of the order of 10 ml to 40 ml, the tubes are made to balance in such a manner that the samples thereof are equal to each other in capacity and mass, and the tubes are then stored into their associated and opposed tube holes respectively formed in the rotor. However, since it cannot be expected that the tubes are made to balance strictly, the motor and rotor are connected through a resilient drive shaft in such a manner that the rotation eccentricity of the rotor caused by the imbalanced samples can be absorbed by the flexing of the drive shaft, whereby the rotor can be rotated at a high speed.
When the imbalance of the samples becomes large, the rotation eccentricity of the rotor cannot be absorbed by the flexing of the drive shaft, so that the drive shaft can be bent or damaged. In order to prevent such problem, there is mounted an imbalance detector such as a displacement sensor for detecting the flexing of the rotation shaft in a non-contact manner, and the swinging amount of the drive shaft is detected by such imbalance detector; and, when the swinging amount of the drive shaft becomes equal to or more than an allowable value, the rotation of the motor is caused to stop. Although the allowable value of the swinging amount of the drive shaft differs according to the diameter dimension of the drive shaft, generally, it is in the range of about 0.4 mm to 0.6 mm. When the imbalance amount of the samples is small, there is a tendency that, as the number of rotations of the motor increases, the swinging amount of the drive shaft increases gradually. In view of this, while changing the time for detecting the sample imbalance according to the allowable value of the drive shaft, the sample imbalance is detected.
Recently, owing to the enhanced strength of the rotor and the enhanced analysis precision of the rotor strength, it has been possible that a bottle of 100 ml to 250 ml can be stored into the rotor. This makes it possible to use, as equipment for producing drugs and reagents, a centrifuge which rotates at a high speed.
In the case of the production equipment, since there are many routine works and simple flow processes to be carried out, sometimes, an operator can omit to store only one bottle into the rotor. In this case, for several dozens to several hundreds of rotations of the rotor, the drive shaft is caused to swing suddenly and greatly. Therefore, even if the rotor is caused to stop when the swinging amount of the drive shaft is in the order of 0.4 mm to 0.6 mm, there is a fear that the drive shaft can be bent. In order to prevent such problem, for hundreds of rotations or less of the rotor, the allowable swinging amount of the drive shaft is lowered down to about 0.2 mm, whereby the sample imbalance due to the omission of storage of the bottle can be detected to thereby prevent the drive shaft from being bent.
However, since the rotor capable of storing bottles each of 100 ml to 250 ml therein is large and heavy, when the rotor is mounted onto the drive shaft, there is a possibility that an operator can oscillate the rotor in error to thereby cause the drive shaft to swing by an amount of about 0.2 mm to 0.4 mm. When the centrifuge is operated in this state, there is a fear that, since the allowable swinging amount of the drive shaft is 0.2 mm for hundreds of rotations of the rotor, the state of the samples can be misunderstood to be imbalanced and thus the centrifuge can be caused to stop. Therefore, an operator must wait for the time (about 60 seconds) until the swinging motion of the drive shaft when mounting the rotor settles down, before the operator starts to operate the centrifuge, thereby lowering the operation efficiency of the centrifuge.
Refer to JP-A-2-74840 and JP-A-2006-7093.
When using a centrifuge as production equipment, preferably, the centrifuge can be rotated just after a rotor is mounted thereon. Thus, it has been desired that, even if a drive shaft is caused to swing when the rotor is mounted onto the drive shaft, the centrifuge can be rotated, and also that the excessive imbalance of samples, which is caused when an operator omits to store one bottle or more into the rotor, can be detected safely.
Thus, it is an object of the invention to provide a centrifuge which can positively detect the excessive imbalance caused by the omission of storage of the bottle and also can be operated just after a rotor is mounted onto a drive shaft, thereby being able to enhance the operation efficiency thereof.